1. Field of the Invention
This invention relates to a limit switch of the type that can be installed in locks and closing devices, but can also be applied as safety switch in doors, windows and be incorporated in other openings that are to be closed and more particularly, to a protective switch for safety belts.
2. Description of the Prior Art
As is known, and even mandatory in several countries, when the safety belt is not used i.e. as long as the lock of the safety belt is open, an electric current circuit is triggered, which activates in the vehicle an optical or acoustical signal, and interrupts the ignition circuit, so that starting the car is not possible. A switch for this purpose must not only be relatively inexpensive but ruggedly constructed, because it is required in large quantities, is used frequently and must be effective with little or no service. Thus a protective switch for safety belts must operate with a high degree of reliability because its failure can disable a vehicle and a malfunctioning of the protective switch may diminish the driver's confidence in the safety belt, and incline him unfavorably against using the safety belt.
It was known to provide switches with a spring-loaded rolling contact as an operating member, for example, a ball contact in the form of a ball bearing, whereby the rolling member either slides toward the contact point or away from it.
The use of rolling bodies as an operating contact member in a limit switch is desirable from a technical consideration because such rolling bodies, for example the contact ball, assure good contact even at very low voltages, due to the rolling action during the operation of the switch. Rolling of the roller and rolling it along the surface of the roller, assures the contact areas to be rubbed and thereby cleaned off of possible oxidation coating. Furthermore, the use of a roller-shaped or ball-shaped switching contact member has the advantage that a relatively high contact pressure per unit area is achieved because of the line-shaped seating of the switching member on the contact.